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DYN AMIC MECHANICAL AN ALYSIS I TESTING MODES & APPLICATIONS
Iso-strain and Iso-stress Tests
In this mode, the strain or stress is held at a constant value and a linear heating rate is applied. These tests are valuable for assessing mechanical behavior under conditions of fixed load
(stress) or fixed deformation (strain). The right figure shows a sample of PET film tested in tension geometry under iso-stress conditions with a linear heating rate followed immediately by an
iso-strain condition and linear cooling rate. It can be observed in the figure that under iso-stress the strain gets larger as the sample is heated and softens. At a temperature of 85°C the
strain is then held constant and as the sample is cooled, the sample stress gets larger. These test modes are ideal for characterization of shape memory materials.
Data Acquisition Interval
90
Time
80
r--. 70
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0
'--"
3
�
60
'0
:J
CD
-
a
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-+
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50
C
(j)
E
CD
t=
40
30
20
Testing Modes and Applications
24
100
r--.
0.!2
'--"
C
'2
-
(f)
10-1
Iso-stress and Iso-strain on PET Film
108
"-
Iso-strain
(f)
-+
(j)
(J)
107
�
"'0
Q
'--"
Iso-stress
106
0 250 500 750
time (s)